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2025 HONDA PROLOGUE
EX Single Motor FWD•FWD•AUTOMATIC•ev
1 active safety recall on this vehicle — view recalls
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Repairs0Labor315Torque67Fluid5DTC809Battery1Maintenance0Recalls1
P0125moderate severityPowertrain

Insufficient Coolant Temperature for Closed Loop Fuel Control

on 2025 Honda Prologue EX Single Motor FWD · FWD

What this code means

The engine is not reaching normal operating temperature quickly enough for the PCM to enter closed-loop fuel control.

Symptoms

  • Check Engine Light
  • Poor fuel economy
  • Extended warmup time
  • Rich exhaust smell

Common causes

  • Stuck-open thermostat
  • Faulty ECT sensor
  • Cooling fan running constantly
  • Low coolant level

Diagnostic steps

  1. Monitor ECT warmup time (should reach 160°F within 5-10 min)
  2. Test thermostat
  3. Check cooling fan operation
  4. Test ECT sensor

Repair notes

Replace thermostat. Most common cause.

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